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Jim Rich, Janete Brito, Jay Ferrell, and Ramandeep Kaur2 1. This document is ENY-060, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date: April 2010. Visit the EDIS Web Site at http://edis.ifas.ufl.edu. 2. Jimmy R. Rich, professor, North Florida REC, Institute of Food and Agricultural Sciences, University of Florida, Quincy, FL 32351; Janete Brito, nematologist, FDACS Division of Plant Industry, and Courtesy Faculty, Entomology and Nematology Department, University of Florida, Gainesville, FL 32611; Jason Ferrell, associate professor, Agronomy Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611; and Ramandeep Kaur, research associate, Department of Plant Pathology, Louisiana State University Agricultrual Center, Baton Rouge, LA 70803. Root-knot nematodes (Meloidogyne spp.) are the most widespread and damaging of the plant-parasitic nematodes found in Florida, and they survive and even thrive on weeds. To date, about 97 root-knot nematode species have been described, but within the genus, M. arenaria, M. incognita, and M. javanica (peanut, southern and Javanese root-knot nematodes, respectively) represent 95% of all root-knot nematode problems in Florida. Other root-knot nematodes found causing problems in specific crops in the state include M. graminis, M. mayaguensis and M. partityla (grass, guava and pecan root-knot nematodes, respectively). Weeds and nematodes are widely present in Florida agro-ecosystems, and the interaction of these primary pests can magnify problems compared to each acting alone. Because weeds are widely present and many are good hosts of root-knot nematodes, weed control is an excellent first step in reducing root-knot nematode damage in Florida agriculture. To determine the status of weeds as hosts of root-knot nematodes, greenhouse and field evaluations were used to measure nematode reproduction of individual nematode and weed combinations. For practical field observations, however, galling on plant roots most times indicates nematode reproduction on a weed or crop plant and generally the greater degree of galling, the greater root-knot nematode reproduction on the plant (Figure 1). The host status and degree of nematode reproduction on weeds is a major concern in developing and implementing integrated nematode management programs because weeds are almost universally present during crop growth and afterwards in fallow periods. This is contrary to modern perceptions of many professionals who now consider that weeds are not major constraints in agricultural production due to the excellent control provided by herbicides. However, weed control is often conducted relative to weed populations and threshold levels established for weed/crop competition. If weed populations are relatively low or grow only late in the season, it may be viewed as unprofitable to perform weed control, regardless of
Weed Hosts of Root-Knot Nematodes Common to Florida 2 Root galling (knots) on Amaranth infected with Guava root-knot nematode (Meloidogyne mayaguensis). whether these weeds are hosts of plant-parasitic nematodes. Additionally, most row crop and vegetable acreage remains fallow for long periods of the year, and weeds grow in abundance during these periods. These fallow periods may last from 3-6 months and are natural in most crop production cycles. For example, in north Florida thousands of acres of cotton and peanut are harvested in September and October each year, and the land may not be used again for crop production for over 6 months until planting commences the following May. Unless controlled during the off-season, weeds may maintain or increase nematode populations. Nematode reproduction on weeds may seem to be a simple problem to solve simply control weeds, particularly in the off-cropping season. However, this could lead to increased grower cost, greater soil erosion potential, less nutrient recycling, and lower soil organic matter levels. Some options to reduce these negative aspects would include selectively eliminating major weed hosts with herbicides (mostly broadleaf weeds), encouraging the growth of non-host weeds (mostly grassy weeds), or planting cover crops that suppress weed populations. It is important to emphasize that without a strong weed management program both in-season and off-season, the benefits of crop rotation for nematode management can be quickly annulled by weed hosts of plant-parasitic nematodes. Knowledge about weeds as hosts of root-knot nematodes, particularly weeds known to be highly symptomatic hosts, makes it possible to use existing weeds to monitor fields for those nematodes. This is especially important when laboratory assays are impractical or when more data points on nematode infestation are needed than can be derived by laboratory soil assay alone. For instance, the citron melon has been used to monitor the peanut root-knot nematode in north Florida fields and several leguminous weed species were used to index a root-knot nematode infestation in fields to be planted to cantaloupes.
Weed Hosts of Root-Knot Nematodes Common to Florida 3 Information presented in Table 1 shows only those weed species found to be hosts to one or more common root-knot nematodes found in Florida. However, it is important to also remember that some weeds are NOT hosts of plant-parasitic nematodes, a fact that may be useful in management programs. For example, UF/IFAS Nematologist Dr. Harlan Rhoades found that a summer cover crop of hairy indigo (Indigofera hirsuta) was a non-host to the southern and Javanese root-knot nematodes as well as the sting nematode (Belonolaimus longicaudatus). In field experiments, hairy indigo rotation was very effective for control of those nematode species in subsequent vegetable crop production. Overall, information on the host range of root-knot nematodes on weeds is incomplete and sometimes contradictory, and many additional studies are necessary to adequately describe this subject. For example, a recent review article stated that weed hosts had only been studied for 14 of the 97 species of root-knot nematodes known worldwide (1). In addition, there are 3479 recognized weed species in the Weed Science Society of America database, suggesting that much is left to be known about weed hosts to root-knot nematodes. Lastly, weeds present in agricultural fields any time during the year may compromise carefully documented and effective rotation systems for nematode management. Thus, weed management both within and after the normal cropping cycle is an overlooked yet critical component of nematode management systems. A more complete listing of weed hosts of root-knot nematodes worldwide may be found in: 1. Rich, J. R, J. A. Brito, R. Kaur, and J. A. Ferrell. 2009. Weed species as hosts of Meloidogyne: A review. Nematropica 39:157-185.
Weed Hosts of Root-Knot Nematodes Common to Florida 4 List of selected Florida weeds, their common names and botanical families occurring as hosts of root-knot nematodes commonly found in Florida. Scientific namex Weed Common name Family Root-Knot Nematodesy Abutilon theophrasti Velvet leaf Malvaceae Ma, Mi, Mj, Mm Acalypha australis Australian acalypha Euphorbiaceae Mi A. setosa Copperleaf Euphorbiaceae Ma, Mi Achillea millefolium Common yarrow Asteraceae M. sp.z Achyranthes aspera Prickly chaff-flower Amaranthaceae Mi Aerva javanica Kapok bush Amaranthaceae Mi Ageratum conyzoides Goat weed Asteraceae M. sp., Alternanthera sessilis Sessile joyweed Amaranthaceae Mi Amaranthus graecizans Tumbleweed Amaranthaceae Mi, M. sp. A. hybridus Smooth pigweed Amaranthaceae Ma, Mi, Mj A. palmeri Palmer amaranth Amaranthaceae Ma, Mi A. retroflexus Redroot amaranth, Amaranthaceae Ma, Mi, Mj, Mm A. spinosus Spiny amaranth Amaranthaceae Ma, Mi, Mj, Mm A. viridis Slender amaranth Amaranthaceae Mi Ambrosia artemisiifolia Common ragweed Asteraceae Ma, Mi Avena spp. Wild Oats Poaceae M. sp. Axonopus affinis Carpetgrass Poaceae Mi Bidens alba Common beggartick Asteraceae Mi B. frondosa Devils'beggar tick Asteraceae Mi B. pilosa Hairy begger tick Asteraceae M. sp., Mj, Mm Bromus secalinus Cheat Poaceae Mi Capsella bursa-pastoris Shepherd's purse Brassicacea M. sp. Celosia argentea Celosia Amaranthaceae Mi Cenchrus spinifex Field sandbur Poaceae Ma, Mi Cerastium fontanum ssp. vulgare Mouse ear chickweed Caryophyllaceae Mi Chamaesyce hirta Garden spurge Euphorbiaceae Mi C. maculate Spotted spurge Euphorbiaceae Ma, Mi C. prostrata Ground spurge Euphorbiaceae M. sp., Mm Chenopodium album Common lambs-quarters Chenopodiaceae Ma, Mi C. murale Nettle-leaf goosefoot Chenopodiaceae Mi Citrullus lanatus citronmelon Cucurbitaceae Ma Cleome viscosa Jasmin del rio Capparaceae Mi Cnidosculus stimulosus Spurge nettle Euphorbiaceae Ma, Mm Commelina benghalensis Benghal dayflower Commelinaceae M. sp. C. communis Asiatic dayflower Commelinaceae M. sp. C. diffusa Spreading dayflower Commelinaceae M. sp. Conyza albida Fleabane Asteraceae M. sp. Crotalaria spectablis Showy crotalaria Fabaceae Ma, Mi Cynodon dactylon Bermudagrass Poaceae Ma, Mi Cyperus sp. Sedge Cyperaceae Mj C. difformis Smallflower sedge Cyperaceae M. sp. C. esculentus Yellow nutsedge Cyperaceae Mi, Ma C. rotundus Purple nutsedge Cyperaceae Ma, Mi C. sanguinolentus Bloodscale sedge Cyperaceae M. sp. Dactyloctenium aegyptium Crowfootgrass Poaceae M. sp.
Weed Hosts of Root-Knot Nematodes Common to Florida 5 List of selected Florida weeds, their common names and botanical families occurring as hosts of root-knot nematodes commonly found in Florida. Scientific namex Weed Common name Family Root-Knot Nematodesy Datura inoxia Sacred dactura Solanaceae Mi D. stramonium Jimsonweed Solanaceae Ma, Mi Daucus carota Wild carrot n Umbelliferae Mi, M. sp. Desmodium sp. Beggarweed Fabaceae Mi Dichondra repens Dichondra Convolvulaceae Ma, Mi, Mj, Mm Digitaria horizontalis Jamaican crabgrass Poaceae Mi D. sanguinalis Large crabgrass Poaceae Ma Echinochloa colona Jungle-rice Poaceae M. sp. Echinochloa crus-galli Barnyard-grass Poaceae Ma, Mi E. muricata Rough barnyard-grass Poaceae Ma E. prostrata Eclipta Compositae Mm Eleusine indica Goosegrass Poaceae Ma, Mi Elymus repens Quackgrass Poaceae M. sp. Emilia sonchifolia Red tassle-flower Asteraceae Mi, Mm Erechtites hieracifolia American burnweed Asteraceae Mi, Mj Euphorbia heterophylla Wild poinsettia Euphorbiaceae Mj E. hirta Asthma plant Euphorbiaceae Mi E. tirucalli Indiantree Euphorbiaceae Mm Fatoua villosa Mulberryweed Moraceae Mm Hydrocotyle bonariensis Pennywort Apiaceae Mm Indigofera sp. Indigo Fabaceae Mj Ipomoea grandifolia Morning-glory Convolvulaceae M. sp. I. hederacea Ivyleaf morning-glory Convolvulaceae Ma, Mi I. quamoclit Cypressvine morning-gloryConvolvulaceae M. sp. I. triloba Three-lobed morning-gloryConvolvulaceae Ma, Mi, Mj, Mm I. tricolor Multicolored morning-gloryConvolvulaceae M. sp., Mm Jacquemontia tamnifolia Small flower morning-gloryConvolvulaceae Ma, Mi Lactuca saligna Willowleaf, lettuce Asteraceae Mi Leontodon hispidus Bristly hawkbit Asteraceae Ma, Mm Lucas aspera Thumba plant Mi Macroptilium lathyroides Phasey bean Fabaceae Ma Malva neglecta Common mallow Malvaceae Mi Medicago lupulina Black medic Fabaceae Mi Melilotus alba White sweetclover Fabaceae Mi Melilotus indica Sourclover Fabaceae M. sp. Mikania micrantha Mile-a-minute Asteraceae M. sp. Mimosa pudica Sensitive Plant Fabaceae M. sp. Mollugo sp. Carpetweed Aizoaceaee Mi Morella faya fayatree Myricaceae M. sp. Nasturtium officinalis Watercress Cruciferae M. sp. Oenothera biennis Common eveningprimroseOnagraceae Ma Oxalis corniculata Creeping woodsorrel Oxalidaceae M. sp. Panicum miliaceum Wildproso millet Poaceae Mi P. repens Torpedograss Poaceae M. sp. Paspalum notatum Bahia-grass Poaceae Ma, Mi
Weed Hosts of Root-Knot Nematodes Common to Florida 6 List of selected Florida weeds, their common names and botanical families occurring as hosts of root-knot nematodes commonly found in Florida. Scientific namex Weed Common name Family Root-Knot Nematodesy Passiflora mucronata Passion flower Passifloraceae Mm Pennisetum purpureum Napiergrass Poaceae Mi Peperomia pellucida Shiny bush, pepper elder Piperaceae M. sp. Physalis spp. Ground cherry Solanaceae Ma, Mi, Mj Physalis angulata Cutleaf groundcherry Solanaceae Ma Phytolacca americana American pokeweed Phytolaccaceae Ma, Mi, Mj, Mm Plantago major Broadleaf plantain Plantaginaceae M. sp. Poa annua Annual bluegrass Poaceae M. sp. Polygonum persicaria Ladysthumb Polygonaceae Mi Phragmites communis Common reed Poaceae M. sp. Portulaca grandiflora Showy purslane Portulacaceae Mi P. oleracea Common purslane Portulacaceae Ma, Mi, Mj, Mm Raphanus raphanistrum Wild radish Brassicaceae M. sp. Richardia brasiliensis Brazil pusley Rubiaceae M. sp. R. scabra Florida pusley Rubiaceae Mi Rumex acetosella Red sorrel Polygonaceae Ma, Mi R. crispus Curly dock Polygonaceae Mi, Ma Senna alata Emperor's candlesticks Fabaceae Mm S. obtusifolia Sickle pod Fabaceae Ma, Mi, Mj, Mm S. occidentalis Coffee senna Fabaceae Mi, Mj, Mm Sesbania sp. Sesban or sesbania Fabaceae Mi, Mj S. aculeate Prickly sesbania Fabaceae Mj Setaria pumila Yellow foxtail Poaceae Ma S. viridis Green foxtail Poaceae Ma, Mi Sida acuta Southern sida Malvaceae Mi S. spinosa Prickly sida Malvaceae Ma, Mi Solanum sp. Nightshade Solanaceae Ma, Mi Solanum americanum American black nightshadeSolanaceae Mi, Mj, Mm S. nigrum Black nightshade Solanaceae Mi, Mj, M. sp. S. torvum Turkeyberry Solanaceae M. sp., Ma S. viarum Tropical soda apple Solanaceae Ma Sonchus oleraceus Common sowthistle Asteraceae Mi, Mj Sorghum bicolor ssp. arundinaceum Wild sorghum Poaceae M. sp. S. halepense Johnsongrass Poaceae M sp. Spergula arvensis Corn spurry Caryophyllaceae M. sp. Spermacoce confusa Button weed Rubiaceae M. sp. Stellaria media Common chickweed Caryophyllaceae Mi, Talinum triangulare Waterleaf Portulacaceae Mm Tamarix gallica Saltcedar Tamaricaceae Mj Taraxacum officinale Common dandelion Asteraceae Ma, Mi Thlaspi arvense Field pennycress Brassicacea Mi Trifolium repens White clover Fabaceae Mi Urena lobata Cadillo Malvaceae Mi, M. sp. Urochloa ramosa Browntop millet Poaceae M. sp. Verbena officinalis Vervain Verbenaceae Mi
Weed Hosts of Root-Knot Nematodes Common to Florida 7 List of selected Florida weeds, their common names and botanical families occurring as hosts of root-knot nematodes commonly found in Florida. Scientific namex Weed Common name Family Root-Knot Nematodesy Veronica spp. Speedwell Scrophulariaceae M. sp. Vicia villosa Hairy vetch Fabaceae Ma, Mi Withania somnifera Ashwagandha Solanaceae Mi Xanthium strumarium Common cocklebur Asteraceae Ma, Mi x Many scientific names of weeds and even family names have changed over the past few years; weed names presented herein are those used by the Weed Science Society of America (http://www.wssa.net/Weeds/ID/WeedNames/namesearch.php). yMa = Meloidogyne arenaria Peanut root-knot nematode; Mi = M. incognita Southern root-knot nematode; Mj = M. javanica Javanese root-knot nematode; Mm M. mayaguensis Guava root-knot nematode. z M. sp. = Species of root-knot nematode not identified.